Multi-chip modules (MCM's) are integrated circuit packages in which multiple semiconductor dies are packaged on the same substrate. MCM's traditionally have dies mounted side by side on a substrate. However, more recently MCM's have been developed in which semiconductor dies are stacked vertically. Such vertically stacked dies have a smaller footprint than conventional MCM's and are often used in applications such as cell phones and tablet computers in which chip space is at a premium. The stacked dies are typically encapsulated in protective epoxy, such as by transfer molding.